Self-supporting electrocatalytic material and preparation method thereof

ABSTRACT

The present disclosure relates to a self-supporting electrocatalytic material and a preparation method thereof, the self-supporting electrocatalytic material is a Cu2O/WO3/CF self-supporting electrocatalytic material. The Cu2O/WO3/CF self-supporting electrocatalytic material comprises: a foamed copper substrate, and Cu2O and WO3 grown in situ on the foamed copper substrate.

TECHNICAL FIELD

The present disclosure relates to a self-supporting electrocatalytic material, in particular to a Cu₂O/WO₃/CF self-supporting electrocatalytic material and a NiOOH/Cu₂O/WO₃/CF self-supporting electrocatalytic material and a preparation method thereof, which belongs to the technical field of composite materials.

BACKGROUND

The electrochemical decomposition of water into hydrogen and oxygen is an effective method for fundamentally realizing the strategy of the conversion and storage of renewable energy, and solving the global energy and environmental problems. In this process, the conversion efficiency is limited by the high overpotential. At present, the noble metal Pt-based materials are considered to be the most effective hydrogen evolution reaction (HER) electrocatalysts, and Ir/Ru and its oxides are considered to show excellent oxygen evolution reaction (OER) electrocatalytic properties in both acidic and alkaline electrolytes. However, due to the low content of these precious metal materials in the earth crust and the high cost, their commercial large-scale application has been limited. The development of new sustainable non-noble metal electrocatalytic materials with low cost and high efficiency is the key.

WO₃ belongs to n-type semiconductors, which are composed of regular octahedral perovskite units, have unique optical, electronic, and chemical properties, and have been widely used in sensors, catalysis, electrochromic, and other fields in recent years. WO₃ material has a fast electron transfer speed (12 cm² V⁻¹ s⁻¹), a suitable hole diffusion length (150 nm), and a wide light absorption range (12%). Therefore, WO₃ is a promising photoelectric catalytic material. However, the WO₃ nanomaterial obtained by current research has some shortcomings such as a small specific surface area, few catalytic active sites, high and unstable hydrogen and oxygen production over-potential, which limits their catalytic activity. Oxygen defects in metal oxides act as active sites to improve conductivity and facilitate the adsorption and desorption of water molecules or intermediate reaction substances (for example, ·H in HER; ·OH and ·OOH in OER), thereby further illustrating that the introduction of oxygen defects into WO₃ materials is expected to improve the electrocatalytic performance of WO₃ materials. At the same time, through processes such as compounding, the electronic structure of WO₃ is adjusted, the oxygen defect content can be effectively increased, so that the electrocatalytic active sites are increased and the electrocatalytic performance is optimized.

At present, the use of copper-based materials for oxygen evolution catalysts has attracted wide attention. Copper-based materials have the advantages of abundant reserves, low cost, and simple synthesis of their compounds. Cu-based metal oxides are good electrode materials. However, although Cu₂O materials are used as photocatalytic materials, there are relatively few studies on their use in electrocatalysis. Therefore, it is necessary to further research and explore Cu₂O electrocatalytic materials. In addition, in order to avoid the influence of the binder on the conductivity and active area of the catalyst during the preparation of the working electrode, the direct synthesis of WO₃ nanostructured catalyst on the conductive substrate can effectively improve the electrocatalytic performance. Foamed copper with high abundance and low price has attracted widespread attention, because of its large specific surface area, high electronic conductivity, and ideal 3D open cell structure, it is widely used as a support system for electrode materials.

Foamed copper is a new multifunctional material with a large number of connected or unconnected pores uniformly distributed in the copper matrix. Foamed copper has good conductivity and ductility, and its preparation cost is lower than that of foamed nickel, and its conductivity is better than that of foamed nickel. It is a potential multi-dimensional carrier for the preparation of battery anode materials, catalysts, and electromagnetic shielding materials. Compared with metal materials, there are many advantages to using highly conductive carbon materials (such as carbon fiber, carbon cloth, carbon paper, etc.) as a carrier, such as their light weight, stable chemical properties, and environmental friendliness, etc. However, due to their good chemical inertness, the compatibility between carbon materials and various inorganic materials is poor, so it is difficult to directly and effectively grow active substances on their surfaces. Therefore, it is of great significance to develop an effective method to directly grow a highly active composite material on the foamed copper conductive substrate and directly use it for electrocatalytic hydrogen production.

SUMMARY

In view of the above problems, the present disclosure provides a new self-supporting electrocatalytic material and a preparation method thereof. The purpose of the present disclosure is to synthesize a high-efficiency hydrogen evolution reaction (HER) electrocatalytic material by adopting a multi-step method, and the structure of the prepared self-supporting electrocatalytic material is controllable, and the product has the structure of a nanowire (WO₃) regular tetrahedron (Cu₂O) and ultra-small nanoparticles (NiOOH) at the same time, and the structures of nanowire, regular tetrahedron and ultra-small nanoparticle are uniformly distributed. The prepared material shows better electrocatalytic performance in neutral solution.

In a first aspect, the present disclosure provides a Cu₂O/WO₃/CF self-supporting electrocatalytic material, comprising: a foamed copper substrate, and Cu₂O and WO₃ grown in situ on the foamed copper substrate.

According to the present disclosure, the foamed copper is used as a copper source for the first time, and a Cu₂O tetrahedral structure and a WO₃ nanowire structure are grown in situ on the surface of the foamed copper substrate by a one-step method, so that the influence of an adhesive on the conductivity and activity of the catalyst during the preparation of a working electrode is avoided, and the electrocatalytic performance can be effectively improved.

Preferably, the total loading capacity of Cu₂O and WO₃ is 0.5 to 4 mg/cm².

Preferably, the molar ratio of WO₃ and Cu₂O is 1:(0.5 to 1).

In a second aspect, the present disclosure provides a Cu₂O/WO₃/CF self-supporting electrocatalytic material. The Cu₂O/WO₃/CF self-supporting electrocatalytic material also includes NiOOH grown in situ on the foamed copper substrate, which is designed as a NiOOH/Cu₂O/WO₃/CF self-supporting electrocatalytic material. In other words, the NiOOH/Cu₂O/WO₃/CF self-supporting electrocatalytic material comprises: a foamed copper substrate, and NiOOH, Cu₂O, and WO₃ grown on the foamed copper substrate. Among them, NiOOH nanoparticles are distributed in both Cu₂O and WO₃.

In the present disclosure, the foamed copper substrate (CF) can improve the exposure of active sites of products due to its high specific surface, high electronic conductivity and 3D open-cell structure, which is beneficial to the improvement of electrocatalytic performance. Therefore, the Cu₂O tetrahedron structure is grown in situ by taking the foamed copper as the copper source for the first time, and the NiOOH and WO₃ are directly grown on the foamed copper substrate (CF) at the same time, so that the influence of the adhesive on the conductivity and activity of the catalyst during the preparation of the working electrode is avoided and the electrocatalytic performance can be effectively improved by utilizing the synergistic effect.

Preferably, the total loading capacity of NiOOH, Cu₂O, and WO₃ in the Cu₂O/WO₃/CF self-supporting electrocatalytic material is 0.5 to 4 mg/cm².

Preferably, the molar ratio of WO₃, Cu₂O, and NiOOH is 1:(0.5 to 1):(0.01 to 0.05).

In a third aspect, the present disclosure also provides a preparation method of the above mentioned Cu₂O/WO₃/CF self-supporting electrocatalytic material, comprising:

-   -   (1) dissolving a tungsten source in absolute ethanol to obtain a         first solution;     -   (2) immersing the foamed copper in a high-pressure reaction         kettle containing the first solution, reacting at 100 to 200° C.         for 1 to 36 hours, and then centrifuging, washing, and drying to         obtain the Cu₂O/WO₃/CF self-supporting electrocatalyst material.

Preferably, the tungsten source is selected from at least one of the ammonium tungstate (NH₄)₆W₇O₂₄·6H₂O, ammonium paratungstate (NH₄)₁₀[H₂W₁₂O₄₂], ammonium metatungstate (NH₄)₆H₂W₁₂O₄₀, tungsten isopropoxide W(OCH(CH₃)₂)₆, and tungsten hexachloride WCl₆; the concentration of the tungsten source in the first solution is 0.01 to 5 mol/L.

Preferably, the volume filling ratio of the high-pressure reaction kettle containing the first solution is 20 to 60%.

In a fourth aspect, the present disclosure also provides a preparation method of the above mentioned Cu₂O/WO₃/CF self-supporting electrocatalytic material, comprising:

-   -   (1) dissolving a tungsten source in absolute ethanol to obtain         the first solution;     -   (2) immersing the foamed copper grown with NiOOH and Cu₂O in a         high-pressure reaction kettle containing the first solution,         reacting at 100 to 200° C. for 1 to 36 h, and then centrifuging,         washing, and drying to obtain a NiOOH/Cu₂O/WO₃/CF         self-supporting electrocatalytic material.

Preferably, the concentration of the tungsten source in the first solution is 0.01 to 5 mol/L.

Preferably, the tungsten source is selected from at least one of ammonium tungstate (NH₄)₆W₇O₂₄·6H₂O, ammonium paratungstate (NH₄)₁₀[H₂W₁₂O₄₂], ammonium metatungstate (NH₄)₆H₂W₁₂O₄₀, tungsten isopropoxide W(OCH(CH₃)₂)₆, and tungsten hexachloride WCl₆.

Preferably, the volume filling ratio of the high-pressure reaction kettle containing the first solution is 20 to 60%.

Preferably, the foamed copper grown with NiOOH and Cu₂O is prepared by:

-   -   (1) dissolving a nickel source in water to obtain a second         solution;     -   (2) immersing the foamed copper in a high-pressure reaction         kettle containing the second solution, reacting at 160 to         200° C. for 6 to 12 hours, and then washing and drying to obtain         the foamed copper with NiOOH and Cu₂O.

Also, preferably, the nickel source is selected from at least one of nickel acetate Ni(CH₃COO)₂, nickel oxalate dihydrate NiC₂O₄·2H₂O, nickel chloride hexahydrate NiCl₂·6H₂O, and nickel nitrate hexahydrate NiN₂O₆·6H₂O; the concentration of the nickel source is 0.01 to 5 mol/L;

Preferably, the volume filling ratio of the high-pressure reaction kettle containing the second solution is 20 to 80%.

Beneficial Effects

-   -   (1) The NiOOH/Cu₂O/WO₃ composite material is synthesized by a         two-step method in the present disclosure. The Cu₂O is in situ         synthesized with foamed copper as a raw material, and the         composite material is directly grown on the foamed copper         substrate; at the same time, the Cu₂O and WO₃ are directly grown         on the foamed copper by a one-step method in the present         disclosure;     -   (2) the present disclosure has mild reaction condition, easy         realization, and easy control of the process;     -   (3) the composite material prepared by the present disclosure         has a large number of oxygen defects;     -   (4) the NiOOH/Cu₂O/WO₃ self-supporting electrocatalytic material         prepared by the present disclosure exhibits better         electrocatalytic performance in a neutral electrolyte.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows X-ray diffraction (XRD) spectra of NiOOH/Cu₂O/WO₃/CF, Cu₂O/WO₃/CF and NiOOH/Cu₂O/CF prepared under the conditions of Example 1, Comparative Example 1, and Example 5;

FIG. 2 shows scanning electron microscope (SEM) photographs of (a-b) NiOOH/Cu₂O/CF and (c-d) Cu₂O/WO₃/CF prepared under the conditions of Comparative Example 1 and Example 5;

FIG. 3 shows a SEM photograph of NiOOH/Cu₂O/WO₃/CF prepared under the conditions of Example 1;

FIG. 4 shows a transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) image of NiOOH/Cu₂O/WO₃/CF prepared under the conditions of Example 1;

FIG. 5 shows a distribution diagram of corresponding elements of NiOOH/Cu₂O/WO₃/CF prepared under the conditions of Example 1;

FIG. 6 shows the O1s spectra of NiOOH/Cu₂O/WO₃/CF, Cu₂O/WO₃/CF, and NiOOH/Cu₂O/CF prepared under the conditions of Example 1, Comparative Example 1, and Example 5;

FIG. 7 shows a comparative graph of the electrocatalytic hydrogen production overpotentials at different current densities for NiOOH/Cu₂O/WO₃/CF, Cu₂O/WO₃/CF, NiOOH/Cu₂O/CF, and CF prepared under the conditions of Example 1, Comparative Example 1, and Example 5.

FIG. 8 shows a Raman spectrum of NiOOH/Cu₂O/WO₃/CF prepared under the conditions of Example 1.

DETAILED DESCRIPTION

The present disclosure will be further described below through the following embodiments. It should be understood that the following embodiments are only used to illustrate the present disclosure, not to limit the present disclosure.

In this disclosure, for the first time, NiOOH, Cu₂O and WO₃ are compounded and directly grown on foamed copper by a two-step method to prepare a NiOOH/Cu₂O/WO₃/CF self-supporting electrocatalytic material rich in oxygen defects. Among them, the optimal total loading capacity of NiOOH/Cu₂O/WO₃ is 0.5 to 4 mg/cm². The molar ratio of WO₃, Cu₂O, and NiOOH is 1:(0.5 to 1):(0.01 to 0.05).

The following exemplarily illustrates the preparation method of the NiOOH/Cu₂O/WO₃/CF self-supporting electrocatalytic material.

Cleaning of the foamed copper substrate. Take a 50 mL beaker, and completely immerse the foamed copper with a length of 3 to 7 cm and a width of 1 to 2 cm into acetone, HCl solution of 2 to 6 mol/L, deionized water, and absolute ethanol in sequence, and carry out ultrasonic treatment for 15 to 30 minutes respectively.

Preparation of foamed copper grown with NiOOH/Cu₂O. The type, concentration, and reaction temperature of the selected nickel source in the present disclosure are very important. The target product phase that is not suitable for the preparation cannot be synthesized, and the product loading is too large or too small, so that the product is difficult to directly grow on the foamed copper or cause the composite product to fall off from the foamed copper in the subsequent composite synthesis stage.

The analytically reagent nickel acetate Ni(CH₃COO)₂ is added as a nickel source to 20 to 80 mL of deionized water, and stirred for 20 to 60 minutes to form a uniformly mixed solution A. Among them, the nickel source can also be selected from nickel acetate Ni(CH₃COO)₂, nickel oxalate dihydrate NiC₂O₄·2H₂O, nickel chloride hexahydrate NiCl₂·6H₂O, and nickel nitrate hexahydrate NiN₂O₆·6H₂O, etc. The concentration of Ni source in the solution A can be 0.01 to 5 mol/L.

The foamed copper is immersed in a polytetrafluoroethylene-lined autoclave containing the solution A and sealed, and the volume filling ratio keeps between 20% and 80%. Putting the sealed high-pressure reactor into a homogeneous hydrothermal reactor, the temperature parameter can be set to 160 to 200° C., and the reaction time can be 6 to 12 hours.

After the reaction is completed, cooling to room temperature, and then centrifuging, washing, and drying to obtain foamed copper with NiOOH/Cu₂O grown on the surface. Among them, washing includes washing with deionized water 3 to 5 times. Among them, drying includes putting the washed foamed copper into a 50 to 70° C. vacuum oven and drying for 5 to 8 hours, or putting in a freeze drying oven at −40 to −60° C. for 5 to 8 hours.

As a tungsten source, analytical reagent ammonium tungstate (NH₄)₆W₇O₂₄·6H₂O is dissolved and added to 20 to 80 mL of absolute ethanol, and stir for 20 to 60 minutes to form a uniformly mixed solution B. Among them, the tungsten source can also be selected from one of ammonium tungstate (NH₄)₆W₇O₂₄·6H₂O, ammonium paratungstate (NH₄)₁₀[H₂W₁₂O₄₂]xH₂O, ammonium metatungstate (NH₄)₆H₂W₁₂O₄₀·XH₂O, and tungsten isopropoxide W(OCH(CH₃)₂)₆ and tungsten hexachloride WCl₆, etc. The concentration of the tungsten source in the solution B can be 0.01 to 5 mol/L.

The NiOOH/Cu₂O-grown foamed copper or pure foamed copper is immersed in a polytetrafluoroethylene lined autoclave containing the solution B and sealed, and the volume filling ratio is maintained between 20% and 60%. Putting the sealed high-pressure reactor into a homogeneous hydrothermal reactor, the temperature parameter can be set to 100 to 200° C., and the reaction time can be 1 to 36 hours.

After the reaction is completed, cooling to room temperature, and then centrifuging, washing, and drying to obtain foamed copper grown with NiOOH/Cu₂O/WO₃ or foamed copper grown with Cu₂O/WO₃. Among them, washing includes washing with deionized water 3 to 5 times. Among them, drying includes putting the washed foamed copper into a vacuum oven at 50 to 70° C. and drying for 5 to 8 hours, or putting in a freeze drying oven at −40 to −60° C. for 5 to 8 hours.

Hereinafter, the present disclosure will be further described with the following examples. It should be understood that the following examples are used to explain this invention and do not mean to limit the scope of this invention. Any non-essential improvements and modifications made by a person skilled in the art based on this invention all fall into the protection scope of this invention. The specific process parameters below are only exemplary, and a person skilled in the art can choose proper values within an appropriate range according to the description, and are not restricted to the specific values shown below.

Example 1

-   -   (1) Prepared a nickel acetate Ni(CH₃COO)₂·4H₂O solution A with a         concentration of 0.05 mol/L. Specifically, Ni(CH₃COO)₂·4H₂O was         added to 40 mL of deionized water and stirred for 30 minutes to         form a uniformly mixed solution A;     -   (2) Put the solution A into a polytetrafluoroethylene lined         autoclave, the volume filling ratio was maintained at 40%;     -   (3) Took a 50 mL beaker, and completely immerse the foamed         copper with a length of 6 cm and a width of 1 cm into acetone, 3         mol/L HCl solution, deionized water, and absolute ethanol in         sequence, and carried out ultrasonic treatment separately for 30         minutes. Put the processed foamed copper into a         polytetrafluoroethylene reactor containing the solution A; put         the sealed reactor into a homogeneous hydrothermal reactor, the         temperature parameter was set to 160° C., and the reaction time         was 12 hours;     -   (4) After the reaction was completed and cooled to room         temperature, the foamed copper after the reaction was taken out         and washed with absolute ethanol and deionized water 3 times;     -   (5) Prepared a solution B of tungsten hexachloride WCl₆ with a         concentration of 0.05 mol/L. Specifically, added WCl₆ to 40 mL         of deionized water and stirred it for 30 minutes to form a         uniformly mixed solution B;     -   (6) Immersed the NiOOH/Cu₂O-grown foamed copper in a         polytetrafluoroethylene lined autoclave containing the solution         B and sealed it, and the volume filling ratio was maintained at         40%. Put the sealed autoclave into a homogeneous hydrothermal         reactor, the temperature parameter was set to 160° C., and the         reaction time was 12 hours;     -   (7) After the reaction was completed, cooled to room         temperature, took out the foamed copper after the reaction, and         washed with absolute ethanol and deionized water 3 times. Put it         into a 60° C. vacuum oven or a freeze-drying oven to dry for 6         hours to obtain a NiOOH/Cu₂O/WO₃/CF self-supporting         electrocatalytic material. The total loading of NiOOH/Cu₂O/WO₃         was 0.86 mg/cm². The molar ratio of WO₃ and Cu₂O was 1:0.5. The         molar ratio of WO₃, Cu₂O, and NiOOH was 1:0.5:0.01.

Example 2

-   -   (1) Prepared a nickel acetate Ni(CH₃COO)₂·4H₂O solution A with a         concentration of 1 mol/L. Specifically, Ni(CH₃COO)₂·4H₂O was         added to 60 mL of deionized water and stirred for 30 minutes to         form a uniformly mixed solution A;     -   (2) Put the solution A into a polytetrafluoroethylene lined         autoclave, the volume filling ratio was maintained at 60%;     -   (3) Took a 50 mL beaker, and completely immersed the foamed         copper with a length of 6 cm and a width of 2 cm in acetone, 4         mol/L HCl solution, deionized water, and absolute ethanol in         sequence, and carried out ultrasonic treatment separately for 30         minutes. Put the processed foamed copper into a         polytetrafluoroethylene reactor containing the solution A; put         the sealed reactor into a homogeneous hydrothermal reactor, the         temperature parameter was set to 200° C., and the reaction time         was 12 hours;     -   (4) After the reaction was completed and cooled to room         temperature, the foamed copper after the reaction was taken out         and washed with absolute ethanol and deionized water 3 times.     -   (5) Prepared a solution B of ammonium tungstate (NH₄)₆W₇O₂₄.6H₂O         with a concentration of 1 mol/L. Specifically, added         (NH₄)₆W₇O₂₄.6H₂O to 40 mL of deionized water and stirred it for         30 minutes to form a uniformly mixed solution B;     -   (6) Immersed the NiOOH/Cu₂O-grown foamed copper in a         polytetrafluoroethylene lined autoclave containing the solution         B and sealed it, and the volume filling ratio was maintained at         40%. Put the sealed autoclave into a homogeneous hydrothermal         reactor, the temperature parameter was set to 140° C., and the         reaction time was 24 hours;     -   (7) After the reaction was completed and cooled to room         temperature, the foamed copper after the reaction was taken out         and washed with absolute ethanol and deionized water 3 times.         Put it into a 60° C. vacuum oven or a freeze-drying oven to dry         for 6 hours to obtain a NiOOH/Cu₂O/WO₃/CF self-supporting         electrocatalytic material. The total loading of NiOOH/Cu₂O/WO₃         in the obtained NiOOH/Cu₂O/WO₃/CF self-supporting         electrocatalytic material was 1.5 mg/cm². The molar ratio of         WO₃, Cu₂O, and NiOOH was 1:0.3:0.03.

Example 3

-   -   (1) Prepared a nickel oxalate dihydrate NiC₂O₄·2H₂O solution A         with a concentration of 3 mol/L. Specifically, NiC₂O₄·2H₂O was         added to 50 mL of deionized water and stirred for 30 minutes to         form a uniformly mixed solution A;     -   (2) Put the solution A into a polytetrafluoroethylene lined         autoclave, the volume filling ratio was maintained at 50%;     -   (3) Took a 50 mL beaker, and completely immersed the foamed         copper with a length of 7 cm and a width of 1 cm into acetone, 3         mol/L HCl solution, deionized water, and absolute ethanol in         sequence, and carried out ultrasonic treatment separately for 30         minutes. Put the processed foamed copper into a         polytetrafluoroethylene reactor containing the solution A; put         the sealed reactor into a homogeneous hydrothermal reactor, the         temperature parameter was set to 180° C., and the reaction time         was 18 hours;     -   (4) After the reaction was completed and cooled to room         temperature, the foamed copper after the reaction was taken out         and washed with absolute ethanol and deionized water for 3         times;     -   (5) Prepared a solution B of tungsten hexachloride WCl₆ with a         concentration of 4 mol/L. Specifically, added WCl₆ to 60 mL of         deionized water and stirred it for 30 minutes to form a         uniformly mixed solution B;     -   (6) Immersed the NiOOH/Cu₂O-grown foamed copper in a         polytetrafluoroethylene lined autoclave containing the solution         B and sealed it, and the volume filling ratio was maintained at         60%. Put the sealed autoclave into a homogeneous hydrothermal         reactor, the temperature parameter was set to 140° C., and the         reaction time was 30 hours;     -   (7) After the reaction was completed, cooled to room         temperature, took out the foamed copper after the reaction, and         washed with absolute ethanol and deionized water 3 times. Put it         into a 60° C. vacuum oven or a freeze-drying oven to dry for 6         hours to obtain a NiOOH/Cu₂O/WO₃/CF self-supporting         electrocatalytic material. The total loading of NiOOH/Cu₂O/WO₃         was 3 mg/cm². The molar ratio of WO₃, Cu₂O, and NiOOH was         1:0.6:0.05.

Example 4

-   -   (1) Prepared a nickel nitrate hexahydrate NiN₂O₆·6H₂O solution A         with a concentration of 4 mol/L. Specifically, NiN₂O₆·6H₂O was         added to 80 mL of deionized water and stirred for 30 minutes to         form a uniformly mixed solution A;     -   (2) Put the solution A into a polytetrafluoroethylene lined         autoclave, the volume filling ratio was maintained at 80%;     -   (3) Took a 50 mL beaker, and completely immersed the foamed         copper with a length of 5 cm and a width of 2 cm into acetone, 6         mol/L HCl solution, deionized water, and absolute ethanol in         sequence, and carried out ultrasonic treatment separately for 30         minutes. Put the processed foamed copper into a         polytetrafluoroethylene reactor containing the solution A; put         the sealed reactor into a homogeneous hydrothermal reactor, the         temperature parameter was set to 160° C., and the reaction time         was 6 hours;     -   (4) After the reaction was completed and cooled to room         temperature, the foamed copper after the reaction was taken out         and washed with absolute ethanol and deionized water 3 times;     -   (5) Prepared a solution B of tungsten isopropoxide W(OCH(CH₃)₂)₆         with a concentration of 2 mol/L. Specifically, added         W(OCH(CH₃)₂)₆ to 40 mL of deionized water and stirred it for 30         minutes to form a uniformly mixed solution B;     -   (6) Immersed the NiOOH/Cu₂O-grown foamed copper in a         polytetrafluoroethylene lined autoclave containing the solution         B and sealed it, and the volume filling ratio was maintained at         40%. Put the sealed autoclave into a homogeneous hydrothermal         reactor, the temperature parameter was set to 160° C., and the         reaction time was 24 hours;     -   (7) After the reaction was completed and cooled to room         temperature, the foamed copper after the reaction was taken out         and washed with absolute ethanol and deionized water 3 times.         Put it into a 60° C. vacuum oven or a freeze-drying oven to dry         for 6 hours to obtain a NiOOH/Cu₂O/WO₃/CF self-supporting         electrocatalytic material. The total loading of NiOOH/Cu₂O/WO₃         was 2.8 mg/cm². The molar ratio of WO₃ and Cu₂O was 1:0.5. The         molar ratio of WO₃, Cu₂O, and NiOOH was 1:0.55:0.03.

Example 5

The preparation process of the Cu₂O/WO₃/CF electrocatalytic material in Example 5 referring to Example 1, the difference was that the Cu₂O/WO₃ foamed copper was obtained only by a one-step solvothermal method, that is, only the steps of step 5 to step 7 in Example 1 were performed, and what was added in step 6 was the foamed copper that had not grown anything. In the obtained Cu₂O/WO₃/CF self-supporting electrocatalytic material, the loading capacity of Cu₂O/WO₃ was 0.7 mg/cm², and the molar ratio of WO₃ and Cu₂O was 1:0.5.

Comparative Example 1

The preparation process of the NiOOH/Cu₂O/CF self-supporting electrocatalytic material in this comparative example 1 referred to Example 1, the difference was that the foamed copper grown with NiOOH/Cu₂O was obtained only by one-step hydrothermal method, that is, only the steps of 1 to 4 of the Example 1 was performed, the solvothermal reaction process of the steps 5 to 7 was not performed. In the obtained NiOOH/Cu₂O/CF self-supporting electrocatalytic material, the loading capacity of NiOOH/Cu₂O was 0.28 mg/cm². The molar ratio of NiOOH and Cu₂O was 0.02:1.

FIG. 1 shows the X-ray diffraction (XRD) spectra of NiOOH/Cu₂O/WO₃/CF, Cu2O/WO3/CF, and NiOOH/Cu2O/CF prepared under the conditions of Example 1, Comparative Example 1, and Example 5, It can be seen from the figure that no other miscellaneous phases exist in the phase synthesized by the invention.

FIG. 2 shows the scanning electron microscope (SEM) photographs of NiOOH/Cu₂O/CF and Cu₂O/WO₃/CF prepared under the conditions of Comparative Example 1 and Example 5. It can be seen that the NiOOH/Cu₂O in Comparative Example 1 are large particles formed by agglomeration of many small nanoparticles dispersing in the rough surface structure. The Cu₂O/WO₃ in Example 5 was a composite structure uniformly dispersed by WO₃ nanowires and Cu₂O tetrahedra. These tetrahedrons were of the same size and were entangled by the interwoven nanowire structure at the same time.

FIG. 3 to FIG. 5 respectively show the SEM photos of NiOOH/Cu₂O/WO₃/CF prepared under the conditions of Example 1, and the element distribution of the tetrahedron and nanowire structure in the NiOOH/Cu₂O/WO₃/CF structure. It can be seen that the microstructure of NiOOH/Cu₂O/WO₃ grown in foamed copper was similar to Cu₂O/WO₃ (FIG. 3 ). The main elements of the tetrahedron were Cu and O, which further proved that the tetrahedral structure was Cu₂O, the nanowire structure was WO₃ (FIG. 5 ), combined with XRD; in addition, it can be seen from FIG. 4 that NiOOH and Cu₂O nanoparticles were uniformly dispersed in the material. The heterojunction surface formed by this WO₃/Cu₂O/NiOOH hierarchical structure was very important for the improvement in electrocatalytic performance.

FIG. 6 shows the O1s spectra of NiOOH/Cu₂O/WO₃/CF, Cu₂O/WO₃/CF, and NiOOH/Cu₂O/CF prepared under the conditions of Example 1, Comparative Example 1, and Example 5. It can be found that the nickel oxide, oxidized cuprous, and tungsten oxide were grown in situ on the foamed copper by a two-step method, and the oxygen defects in the product were significantly increased, which also further proved that NiOOH was effective for the increase in content of oxygen defects, compared with Cu₂O/WO₃/CF and NiOOH/Cu₂O/WO₃/CF composite materials.

FIG. 7 shows a comparative graph of the electrocatalytic hydrogen production overpotentials at different current densities for NiOOH/Cu₂O/WO₃/CF, Cu₂O/WO₃/CF, NiOOH/Cu₂O/CF, and CF prepared under the conditions of Example 1, Comparative Example 1, and Example 5. The obtained electrocatalytic materials were respectively placed into a neutral electrolyte (1M KH₂PO₄+1M K₂HPO₄) for electrocatalytic testing. It can be seen that the NiOOH/Cu₂O/WO₃/CF electrocatalytic composite material with rich oxygen defect prepared by the present disclosure had the smallest overpotential under different current densities, and its surface had the best hydrogen production performance. At high current densities of 100, 200, 300, 400, and 500 mA/cm², its overpotentials were respectively 294, 386, 464, 533, and 589 mV. 

The invention claimed is:
 1. A Cu₂O/WO₃/CF self-supporting electrocatalytic material, comprising: a foamed copper substrate, and Cu₂O and WO₃ grown in situ on the foamed copper substrate.
 2. The Cu₂O/WO₃/CF self-supporting electrocatalytic material according to claim 1, wherein the total loading capacity of Cu₂O and WO₃ is 0.5 to 4 mg/cm².
 3. The Cu₂O/WO₃/CF self-supporting electrocatalytic material according to claim 1, wherein the molar ratio of WO₃ and Cu₂O is 1:(0.5 to 1).
 4. The Cu₂O/WO₃/CF self-supporting electrocatalytic material according to claim 1, wherein the Cu₂O/WO₃/CF self-supporting electrocatalytic material also includes NiOOH grown in situ on the foamed copper substrate.
 5. The Cu₂O/WO₃/CF self-supporting electrocatalytic material according to claim 4, wherein the total loading capacity of NiOOH, Cu₂O, and WO₃ in the Cu₂O/WO₃/CF self-supporting electrocatalytic material is 0.5 to 4 mg/cm².
 6. The Cu₂O/WO₃/CF self-supporting electrocatalytic material according to claim 4, wherein the molar ratio of WO₃, Cu₂O and NiOOH is 1:(0.5 to 1):(0.01 to 0.05).
 7. A preparation method of the Cu₂O/WO₃/CF self-supporting electrocatalytic material of claim 1, comprising: (1) dissolving a tungsten source in absolute ethanol to obtain a first solution; and (2) immersing the foamed copper in a high-pressure reaction kettle containing the first solution, reacting at 100 to 200° C. for 1 to 36 hours, and then centrifuging, washing, and drying to obtain the Cu₂O/WO₃/CF self-supporting electrocatalyst material.
 8. The preparation method according to claim 7, wherein the tungsten source is selected from at least one of ammonium tungstate (NH₄)₆W₇O₂₄·6H₂O, ammonium paratungstate (NH₄)₁₀[H₂W₁₂O₄₂], ammonium metatungstate (NH₄)₆H₂W₁₂O₄₀, tungsten isopropoxide W(OCH(CH₃)₂)₆, and tungsten hexachloride WCl₆, and the concentration of the tungsten source in the first solution is 0.01 to 5 mol/L.
 9. The preparation method according to claim 7, wherein the volume filling ratio of the high-pressure reaction kettle containing the first solution is 20 to 60%.
 10. A preparation method of the Cu₂O/WO₃/CF self-supporting electrocatalytic material of claim 4, comprising: (1) dissolving a tungsten source in absolute ethanol to obtain a first solution; and (2) immersing the foamed copper grown with NiOOH and Cu₂O in a high-pressure reaction kettle containing the first solution, reacting at 100 to 200° C. for 1 to 36 hours, and then centrifuging, washing, and drying to obtain a NiOOH/Cu₂O/WO₃/CF self-supporting electrocatalytic material.
 11. The preparation method according to claim 10, wherein the foamed copper grown with NiOOH and Cu₂O is prepared by: (1) dissolving a nickel source in water to obtain a second solution; and (2) immersing the foamed copper in a high-pressure reaction kettle containing the second solution, reacting at 160 to 200° C. for 6 to 12 hours, and then washing and drying to obtain the foamed copper with NiOOH and Cu₂O.
 12. The preparation method according to claim 11, wherein the nickel source is selected from at least one of nickel acetate Ni(CH₃COO)₂, nickel oxalate dihydrate NiC₂O₄·2H₂O, nickel chloride hexahydrate NiCl₂·6H₂O, and nickel nitrate hexahydrate NiN₂O₆·6H₂O, the concentration of the nickel source is 0.01 to 5 mol/L, and the volume filling ratio of the high-pressure reaction kettle containing the second solution is 20 to 80%. 